SINGAPORE - The downpour that lasted for almost an hour on Tuesday brought relief to many.
It also brought hail - to Bukit Batok, Jurong and other western parts of Singapore. And for the next three days, Singapore can expect thunderstorms mostly in the afternoon.
So, did cloud seeding cause the hail and was the rain toxic? Meteorological experts from the National Environment Agency (NEA) address these concerns.
Q: What is hail?
It is a form of moisture in the air that comprises irregular lumps of ice measuring between 0.5cm and 5cm in diameter.
Hail forms in strong thunderstorm clouds, where a good portion of the cloud layer is below freezing point. It is less common in the tropics despite high frequency of thunderstorms.
Based on newspaper reports, the last occurrence of hail in Singapore was on Sept 12, 2009.
Q: Was the hail yesterday caused by the cloud seeding in Indonesia?
No. Clouds do not travel that far. If they did, then they would be going in the wrong direction as the wind is currently blowing the haze away from Singapore.
Q: With the haze and particulates in the air, was it acid rain yesterday?
No. Acid rain is produced from sulphur dioxide that travels a long distance and when it oxidises, it becomes sulphate that comes out as sulphuric acid.
Sulphur dioxide does not come from forest fires, so there is no reason to believe that yesterday's downpour was acid rain.
Q: Was yesterday's rain toxic?
No. The fires from the peat do not result in toxic rain.
What the experts are most concerned about is the particulate matter during the haze.
Q: Did the downpour help clear the particulates from the air?
No. Studies have shown that rain does not effectively scrub out PM2.5, unlike PM10. PM2.5 - fine particles with diameters less than 2.5 micrometres - takes longer to be removed.
The NEA does not know what impact the rain has on the PSI and the PM2.5 levels.
Q: Has there been any recorded death resulting from respiratory problems due to the haze?
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